It is often desirable and frequently absolutely necessary to sample or test a portion of tissue from humans and even animals to aid in the diagnosis and treatment of patients with cancerous tumors, premalignant conditions and other diseases or disorders. Typically in the case of cancer or the suspicion of malignant tumors, a very important process call tissue biopsy is performed to establish whether cells are cancerous.
Biopsy may be done by an open or closed technique. Open biopsy removes the entire tissue mass or a part of the tissue mass. Closed biopsy on the other hand is usually performed with a needle-like instrument and may be either an aspiration (hollow needle on a syringe) or a core biopsy (special tissue cutting needle design). In needle aspiration biopsy, individual cells or clusters of cells are obtained for cytologic examination. In core biopsy, a segment of tissue is obtained for histologic examination which may be done as a frozen section or paraffin section.
The methods and procedures of obtaining tissue samples for cytologic or histologic examination have been performed historically by manual insertion and manipulation of the needle. These procedures are performed "blind" by the physician and guided by "feel" and known anatomic "landmarks".
Tumors are first noted in a patient by one of three ways, palpation, X-ray imaging or Ultrasound imaging. Once a tumor is identified, a biopsy procedure is performed. Modern medical opinion dictates early detection of cancer increases the likelihood of successful treatment.
Two very important innovations in the field of medical technology have influenced the field of tissue biopsy in the last five years. One, the use of tissue imaging devices which allow the physician to "see" inside the body and visually guide the needle to the tumor mass. Two, The invention of Automatic Core Biopsy Devices (ACBD). The ACBD is an instrument which propels a needle set with considerable force and speed to pierce the tumor mass and collect the tissue sample. This ACBD device has allowed physicians to test tissue masses in the early stages of growth and has contributed to the medical trend of early diagnosis and successful treatment of cancer.
Examples of such ACBD devices have been described and used for obtaining tissue samples in U.S. Pat. Nos. 4,651,752; 4,702,260; and 4,243,048.
ACBDs have adapted the use of the manual Tru-Cut.TM. needle set developed by the Travanol company to obtain a "core" of tissue from the biopsy site. The Tru-Cut.TM. needle is comprised of an inner stylet with a semi-circular notch ground away at the distal end with an outer hollow cutting cannula. The stylet is advanced into the tissue and followed by the cannula which cuts and traps the tissue sample in the notch of the stylet. The Tru-Cut.TM. needle yields a core sample which is semi-circular in cross section with it's length determined by the length of the notch.
The stylet is the inner needle on the set with a notched cut out at the distal end. The cannula is the hollow needle of the set with an angled cutting surface at the distal end which slides over the stylet. When the stylet is pushed into tissue, the tissue is pierced and relaxes or prolapses into the notched cut out. When the cannula is slid forward, the tissue in the notch of the stylet is sliced off and retained in the notch until the cannula is drawn back.
The most common Tru-Cut.TM. needle sizes used for manual and ACBD applications are 18, 16 or 14 gauge with a sample length of 17 mm. The Tru-Cut.TM. set is limited to these sizes due to the design limitation of the cross-sectional material strength created by the grinding of the semi-circular notch. Use of the Tru-Cut.TM. needle design in smaller gauges or needles with longer notch lengths, would most likely cause bending or breaking of the stylet at the cross-section of the notch grind as the stylet entered the body. This potential bending or breaking would occur due to the forces created on entry and subsequent advancing of the stylet though the tissues of the body.
An additional limitation to the Tru-Cut.TM. needle design is its limited ability to allow tissue to prolapse into the notch at the time the stylet enters the biopsy site due to the geometry of the notch grind. The semi-circular notch grind across the approximate center line of the stylet diameter only allows prolapsing of tissue to occur from above the notch grind parallel to the notch surface. Since the grind occurs across the approximate centerline of the stylet diameter, tissue cannot prolapse into the notch detail from the sides of the notch, perpendicular to the ground surface. This limitation causes this design to have difficulty in obtaining adequate tissue in biopsy sites where the density of the tissue is very soft and in areas where the density is very stiff or hard without using large gauge needles such as 14 gauge.
This design limitation creates a situation of compromise between the physician's desire to use the smallest least invasive needle gauge and the pathologist's needs for as large a tissue sample as possible to minimize false-positive diagnosis.
The requirements of the physician and the pathologist dictates the need for an alternative approach in the function and design of the needle sets used in manual and ACBD devices. The ideal product would allow the use of smaller needle gages and/or longer samples required from a given biopsy site to obtain the necessary tissue required to make a diagnosis.